Nitrogen: is it a SIDE issue?

Abstract

Dairy farming has borne the brunt of recent public criticism from anglers and others regarding the desire we all share to keep our country green and our rivers and lakes clear. Much of the focus has been on nitrogen and especially the leaching of nitrate into rivers, lakes and groundwater. Nitrate contamination of rivers and lakes, termed ‘eutrophication’, may cause an increase in weed and algae growth. This can make it difficult for boating or swimming and will also require more frequent cleaning of ditches. Fishing may also be affected because fish cannot survive in water that is overloaded with weed and algae growth. The other main risk of nitrate pollution of surface and groundwater is to human health. A high concentration of nitrate in drinking water is a health hazard, particularly for infants. The Ministry of Health has therefore set a maximum acceptable value of 11.3 mg N/L for drinking water in New Zealand. This paper will address four key questions: • Is nitrogen pollution solely a dairy farming (or SIDE) issue? • Is fertiliser use or animal waste the main nitrogen problem in dairying? • How does New Zealand’s nitrogen use compare internationally? • How do we use nitrogen without risk to the environment?